Page 55 from: October 2014

55October 2014

fore only fractions which are clearly distin-

guishable by colour – such as copper and brass

– can be separated.

An alternative to sink-float
All grey heavy metals such as zinc, lead, nickel

and stainless steel cannot be sorted using this

approach. Furthermore, sorting by colour

camera is very inefficient in cases of surface

contamination and colour impurities. Sorting

tests and experience with different input mate-

rials have shown that only a part of the copper

and brass fraction is also optically recognisable.

Only about one-third of the copper and brass

fraction corresponds to the colour definitions

of these two non-ferrous metals. The remain-

ing two-thirds of the total fraction remains

unidentified owing to surface contamination

and is therefore not sorted within the heavy

metal fraction.

X-ray transmission (XRT) technology is also

limited in its sorting efficiency and can there-

fore only be regarded as an alternative to the

sink-float separation process. The transmission

technology ‘shines through’ the material and is

based on the detection of density differences

(an X-ray image is a very good comparison).

Dense material such as lead weakens the X-rays

much more than less dense material, like tissue.

XRT is a kind of density sorting such as the

sink-float process.

Far beyond glass
Another sensor-based possibility involves sort-

ing via X-ray fluorescence (XRF). A few years

ago, Austrian company Redwave developed a

sensor-based sorting system based on X-ray

fluorescence in co-operation with Olympus, a

global market leader in portable XRF systems

for rapid on-site measurements.

Redwave supplies optical sorting machines to

the environmental and mineral industries but

also offers complete plant set-ups from a single

source – from the planning through to the com-

missioning. The sorting system, called Redwave

XRF, was initially used in the field of glass sort-

ing, more precisely for the separation of heat-

resistant and leaded glass from waste glass cul-

let. Soon it became apparent that the potential

fields of application extended far beyond the

glass sector. The use of this technology, togeth-

er with the development of a new machine

design, ‘set new standards in metal sorting, in

particular the sorting of non-ferrous metals’,

the company says. By using this technology, it

is also possible to separate material which, up

to now, was considered unsortable.

Particularly versatile
As regards application possibilities within

metal sorting, XRF technology is particularly

versatile. For example, nickel-based stainless

steels can be separated from nickel-free stain-

less steels (the same applies to molybdenum-

based stainless steels); gold, silver, platinum and

other precious metals can be sorted out of a

mixture of scrap metals; and aluminium can

be separated from heavy metals as well as single

heavy metals into pure fractions.

The sorting of Zorba offers a particularly good

example. Zorba is usually composed of more

than 70% aluminium, mixed with brass, zinc,

copper, ferrous and stainless steels in different

percentages, as well as accompanying metals

such as lead and silver alloys. Using the ZZZ

sorting machine, it is possible to gain all com-

ponents of Zorba according to type and to sort

aluminium on the basis of the alloying ele-

ments copper, zinc and ferrous. In the first sort-

ing step, all metals besides aluminium are

separated to generate two fractions – a heavy

metal fraction and aluminium. Then, all heavy

metals are recovered in an off-line set operation

and the high-grade and precious metals such

as copper, brass, zinc and stainless steel are fed

directly to the recycling process as secondary

raw materials.

It is also possible to further separate the alu-

minium fraction from the first sorting step.

Based on the detection of the alloying compo-

nents copper, zinc and ferrous in the alumini-

um alloys, it is possible to separate aluminium

alloys which are rich in copper, zinc and fer-

rous. The generated pure aluminium fraction

corresponds to the primary aluminium qual-

ity 6061 and can be directly recycled. Through

this sorting process, there is no need for pre-

cious heavy metals either to be sorted manu-

ally or to be exported to low-wage countries.

The sorting of Zurik is similar to that for Zorba.

First of all, the Zurik fraction is separated from

metals which are harmful or undesirable to the

Function principle of XRF sorting machine.

RI8-Alu sorting.indd 55 06-10-14 17:41